Included within the design of electronic chips and transceivers are a number of functional blocks. A functional block is a predetermined portion of the circuit having a surface area less than the total surface area of the circuit. A functional block includes one or more of the circuit's electrical components and may or may not be physically identifiable from a visual inspection of the manufactured circuit. Thus, the perimeter of a functional block may be identified by a grid superimposed on a circuit diagram, or may be identified by physical characteristics of the manufactured circuit. Physical characteristics may include grid lines painted or formed on the manufactured circuit, as well as electrical components that are different colors.
Generally, each functional block contains a plurality of test pads that are connected to a corresponding plurality of the block's internal electrical components. For example, as shown in FIG. 1, a plurality of test pads 101, 103 and 105 are coupled to a corresponding plurality of electrical components 107, 109, and 111 that are included within functional block 100.
A disadvantage of this approach is that the input and output of the functional block as a whole cannot be easily measured using a single test pad associated with the functional block. Instead, the functionality of each electrical component within the functional block has to be tested either by using the plurality of test pads or by breaking out individual lines. A further disadvantage is that associating multiple test pads within each functional block consumes the chip's valuable surface area. Yet another disadvantage is that the approaches outlined above do not offer an apparatus or a method of testing or monitoring the input and output of a functional block, or individual components thereof, using a single test pad associated with that functional block.